Breakfast choice: An experiment combining a nutritional training workshop targeting adolescents and the promotion of unhealthy products.

A randomised control trial was conducted to determine changes in the food and drink choices of adolescents following their participation in a 50-min nutrition workshop. The experiment was conducted at 104 schools in Barcelona (126 classes, 3,291 adolescents). Schools were randomly selected and stratified by district and by public or private status. The students were given three types of vouchers with different options regarding the type of food for which the vouchers could be exchanged (standard for healthy food and drink, two for one for unhealthy food, and two for one for unhealthy drink). Difference-in-differences linear models that control for individual, family, school or neighbourhood characteristics, and the influence of peers were applied. The probability of students' choosing unhealthy food and drink fell by 7.1% and 4.4%, respectively, following participation in the nutrition workshop. The promotion of unhealthy beverages counteracted the positive impact of the workshop on beverage choice.